A wide variety of organic solvents, such as, but not limited to: petroleum solvents; halogenated hydrocarbons; aromatic and aliphatic hydrocarbons; ethers, esters and mixtures thereof, are used for treating or cleaning fabricated parts, for cleaning metal surfaces before painting, cleaning of painting equipment, cleaning of clothing and in particular, in one embodiment, solvents are employed for the removal of ink and other particulates from solvent-based wash solutions, such as for cleaning components of printing presses, like blankets, that come in contact with inks.
For example, during printing on offset presses, the printing cylinder blankets can accumulate foreign matter, such as dried ink or ink build-up, paper, lint, clay, dirt and the like, which must be removed to maintain quality printing. As a result thereof, during a specific run or printing job, the blankets must be cleaned at various times. The blankets also must be cleaned to remove the image when a particular printing job is completed. For this purpose, blanket washers are utilized which spray mixtures of water, cleaning solvents, and wetting agents onto the printing cylinder blanket to effect the cleaning operation.
Since the waste effluent from such blanket washers consists of solvent and water, as well as the foreign matter removed from the blanket, it is highly toxic and cannot be discharged to the sewer. The transportation and disposal of such materials as a hazardous waste is becoming increasingly more expensive. Moreover, since the solvents used in the cleaning operation are relatively expensive, it is desirable to reclaim the solvents for reuse.
One method used in reclamation of solvents from the waste effluent of printing blanket washers has utilized large gravity settling tanks and carbon bed filters. The waste effluent is accumulated in the settling tank in order to permit the solvents, which typically are hydrocarbon or petroleum based, to rise to the top, and the water then is bled from the bottom of the tank and passed through one or more of the carbon bed filters which absorb and remove remaining solvent and other organic contaminants in the water prior to draining. The solvent similarly is directed through such filter beds for removing impurities. Not only are such settling tanks and filter beds relatively bulky and expensive, they often have been problem prone and ineffective. Because of surfactants and wetting agents used with the cleaning solvents in the blanket washing operation, the resulting waste effluent frequently is an emulsion of the water and solvent that does not readily separate in the settling tank, which in turn can impede the effectiveness of the carbon bed filters. As a result, the clarified water still may retain such high levels of solvent as to prevent its direct discharge to the sewer. Continued use of contaminated solvents, furthermore, can result in clogging of the filter beds and costly shutdowns, maintenance and clean up. While various distillation techniques are available for separating solvents from waste effluents, such systems are expensive and complicated, energy inefficient and require heating that can create safety hazards.
Various solvents containing particulates are cleaned by passing them through filtration materials that has a pore size equal to or generally less than 0.2 microns in diameter. These filters hold back the particles and large molecules, while allowing the clarified solvents in the permeate to pass through the small pore sizes. With these small pore sizes, the filters clog very quickly unless a cross flow of fluids is employed. Generally, the cross flow of fluid runs parallel to the filter membrane surface and acts to scrub the filter membrane surface free of trapped particulate matter, and thereby allows the filter pores to remain open sufficiently to permit clarified solvent to pass through the filtration membrane material. This method of liquid solvent clarification is well known in the process filtration industry and is used extensively for the cleaning of water and water-based solutions, and is generally referred to as ultrafiltration or cross flow microfiltration. For example, a method and apparatus for separating water and water-soluble substances from hydrocarbons and halogenated hydrocarbons employing filters is disclosed in U.S. Pat. No. 4,886,603, issued Dec. 12, 1989.
It is desirable to provide for a new, improved, effective system and method for the cleaning of particulate and solvent waste solutions, particularly, but not limited to, solvent-water-particulate wash solutions used for cleaning components of printing presses.